In the class of hearing aids generally referred to as implantable hearing aids, some or all of various hearing augmentation componentry is positioned subcutaneously on or within a patient's skull, typically at locations proximate the mastoid process. In this regard, implantable hearing aids may be generally divided into two sub-classes, namely semi-implantable and fully implantable. In a semi-implantable hearing aid, components such as a microphone, signal processor, and transmitter may be externally located to receive, process, and inductively transmit an audio signal to implanted components such as a transducer. In a fully implantable hearing aid, typically all of the components, e.g. the microphone, signal processor, and transducer; are located subcutaneously. In either arrangement, an implantable transducer is utilized to stimulate a component of the patient's auditory system.
By way of example, one type of implantable transducer includes an electromechanical transducer having a magnetic coil that drives a vibratory actuator. The actuator is positioned to interface with and stimulate the ossicular chain of the patient via physical engagement. (See e.g. U.S. Pat. No. 5,702,342). In this regard, one or more bones of the ossicular chain may be made to mechanically vibrate, causing the vibration to stimulate the cochlea through its natural input, the so-called oval window.
In the case of implantable transducers designed to interface with the ossicular chain, precise control of the engagement between the implantable transducer and the ossicular chain is important for proper transducer operation. For instance, stimulation of the ossicular chain, such as through vibration, relies at least in part on the appropriateness of the interface between the ossicular chain and transducer. Overloading or biasing of the implantable transducer relative to the ossicular chain can result in degraded performance of the biological aspect (movement of the ossicular chain) as well as degraded performance of the mechanical aspect (movement of the actuator). Similarly, if the implantable transducer is underloaded relative to the ossicular chain, e.g. a loose connection or no physical contact at all, vibrations may not be effectively communicated.
In this regard, at the time of implant, proper setup of an implantable transducer may depend on the present condition of the middle ear. For instance, the positioning of the transducer and the nature of the speech processing parameters may be determined based on patient specific biological aspects such as, damage or reduced mobility of the ossicular chain etc. Over time, however, such aspects may change, as well as, additional aspects may develop. These changes or developments, in turn, may affect the performance of the implanted transducer, e.g. such as by changing the engagement between the transducer and the ossicular chain.
In the field of audiometric screening and diagnosis, techniques have been designed to provide information relating to hearing function without active participation by a patient, such as may be desirable for infant patients. One such technique involves detection of transient evoked otoacoustic and/or otovibratory cochlear emissions in response to a resonant test signal provided to the patient. Otoacoustic emissions are sound pressure waves in a gaseous medium emitted from the cochlea. Similarly, otovibratory emissions are mechanical sound vibrations emitted from the cochlea. Such emissions are generated within the cochlea in response to a resonant acoustic stimulus after a latency period of typically 5–20 milliseconds.